Moiré techniques are optical methods for form and surface measurement and characterization. They can be used to measure in-plane deformation and strain, as well as out-of-plane deformation and profilometry. In-plane measurements are usually performed by attaching a grating to an object and then measuring the deformation of the grating. Out-of-plane measurements are usually based on illuminating the object with structured light, which is typically a straight-line grating, and measuring the deformation of reflected light from the object. In both cases, the reflected light can be summed or multiplied by another grating to form a moiré fringe pattern, or the deformation can be measured directly.
There are different moiré techniques, including fringe projection, shadow moiré, projection moiré, and reflection moiré. These are illustrated in FIG. 1.
In fringe projection, a fringe pattern (e.g. parallel lines) is projected onto the object and the projected fringe pattern is captured from another angle. The fringe pattern will be distorted according to the profile of the object. The distance between contours of acquired fringe pattern depends on the pitch of projected fringe pattern and the parameters of fringe projection setup. By analyzing the acquired fringe pattern and knowing the parameters of the fringe projection setup, the profile of the object is calculated.
Shadow moiré uses a grating in front of the object. A collimated light passes through the grating and makes a shadow of the grating on the object. This shadow is captured from different angles through the grating, which produces a moiré pattern.
Projection moiré uses two different gratings, instead of one, one in front of a collimated light source and the other one in front of a camera. The profile of the object is calculated from the moiré pattern and the parameters of the projection moiré setup.
Reflection moiré uses one grating in front of the light source. The structured light is reflected back from a specular object and captured by the camera. The deformation of the structured light (i.e. grating) is related to the slope distribution of the object profile.
What are still needed in the art, however, are profilometry systems and methods that can be used with very bright or very dark objects, with extreme levels of reflection or no reflection, using ultraviolet (UV), visible, near infrared (NIR), or infrared (IR) light and heat, or visible or UV light and fluorescence.